International patent application WO 2005/017278 discloses an articulated arm for awnings of the type described above, formed by a forearm and an arm articulated in an elbow by means of an articulation device. This articulation device comprises a forearm elbow part and an arm elbow part. The forearm elbow part defines a fork between the branches of which a core configured around an axis is fixedly supported. In the mentioned core there is formed an anchoring configuration adapted to couple an enlarged end of the mentioned flexible tie rod element connected to said elastic traction member. The mentioned flexible tie rod element is described in patent ES-A-2159211. The arm elbow part defines a surrounding wall arranged around the core, a clearance being provided between both to accommodate said flexible tie rod element.
To guide a relative rotation between the forearm and arm elbow parts around said axis, and to support the forearm on the arm in a cantilevered manner, the articulation device includes bearing means formed by a pair of annular parts, made of a plastic material, assembled on the surrounding wall of the arm elbow part. These annular parts define a pair of first conical surfaces which in an operative situation face one another and are in contact with a corresponding pair of second conical surfaces formed in the core and in a centering part, respectively, which are integral with the forearm elbow part. The first and second conical surfaces are conjugated and provided for a relative sliding.
A tubular shank coaxial with the axis is inserted in a hollow interior of the core. One of the branches of the fork of the forearm elbow part defines a hole for an end of said shank and the other branch of the fork defines an opening into which the mentioned centering part is fitted, which centering part in turn has a hole for the other end of the shank. The centering part is configured to block the rotation of the core. Once the assembly is completed, the ends of the shank are flared against the holes in the branch of the fork and the centering part, whereby the shank is retained and the assembly is firmly packed.
This construction has several drawbacks. For example, the forearm and arm elbow parts, as well as the core and the centering part, are generally obtained by the injection molding of a lightweight metal alloy, such as aluminium, and the correct adjustment of the conical surfaces demands strict manufacture and assembly tolerances that are difficult to achieve by means of such molded aluminium parts without a subsequent machining. The lack of a correct adjustment can give rise to squeaks while bending and straightening the elbow. Furthermore, a play, however small it is, in the articulation of the elbow can cause a misalignment of the correct position of the forearm with respect to the arm, and this can create interferences, for example, when the articulated arm must be automatically introduced in a bent position into a box during an operation for drawing in the awning. This misalignment will be greater the longer the forearm is. Therefore, a lack of adjustment in the articulation of the elbow limits the maximum length that the forearm can have to be supported in a cantilevered manner by the bearing means in a suitable position. In addition, the friction forces existing in the articulation device for the elbow are to the detriment of the force exerted by the elastic traction member, and as a result there is a decrease in the tension of the canvas.
It is therefore desirable to increase the adjustment and precision to a maximum and to decrease the friction forces to a minimum in the bearing means of the articulation device for the elbow of an articulated arm for an awning.